For an exothermic reaction

Options

A. `H_p` of the products is less than `H_r` of the reactants
B. `H_p` of the products is more than `H_r` of the reactants
C. `H_p` of the products is equal to `H_r` of the reactants
D. `triangleH` is always positive

Answer

To solve the problem regarding the relationship between the enthalpy of products (Hp) and the enthalpy of reactants (Hr) in an exothermic reaction, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Exothermic Reaction**:
An exothermic reaction is one that releases heat to the surroundings. This means that the energy of the products is lower than the energy of the reactants.

2. **Identify the Change in Enthalpy (ΔH)**:
For an exothermic reaction, the change in enthalpy (ΔH) is negative. This can be expressed as:
\[ \Delta H = H_p - H_r \]
where \( H_p \) is the enthalpy of the products and \( H_r \) is the enthalpy of the reactants.

3. **Set Up the Equation**:
Since we know that ΔH is negative for an exothermic reaction, we can rewrite the equation:
\[ H_p - H_r < 0 \]

4. **Rearranging the Equation**:
Rearranging this inequality gives us:
\[ H_p < H_r \]
This indicates that the enthalpy of the products (Hp) is less than the enthalpy of the reactants (Hr).

5. **Conclusion**:
Therefore, for an exothermic reaction, the correct relationship is:
\[ H_p < H_r \]
This means that the enthalpy of the products is lower than that of the reactants.

### Final Answer:
The correct option is (A): \( H_p < H_r \).